Dromiacea
Encyclopedia
Dromiacea is a group of crab
s, ranked as a section. It contains 240 extant and nearly 300 extinct species. Where they are considered to form a monophyletic group, Dromiacea and two other groups of crabs, namely the Raninoida and Cyclodorippoidea
, may be collected together into the Podotremata
, each at the rank of subsection; morphological and molecular evidence argue against such a grouping.
The larva
e of Dromiacea resemble those of the Anomura
more closely than those of other crab
s. This may simply reflect their basal position
in the crab phylogeny.
The fossil record of Dromiacea reaches back at least as far as the Jurassic
, and, if Imocaris is indeed a member, into the Carboniferous
.
The superfamily Eocarcinoidea
, containing Eocarcinus
and Platykotta
, was previously considered to be a member of the Dromiacea, but has since been transferred to the Anomura
.
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, ranked as a section. It contains 240 extant and nearly 300 extinct species. Where they are considered to form a monophyletic group, Dromiacea and two other groups of crabs, namely the Raninoida and Cyclodorippoidea
Cyclodorippoidea
Cyclodorippoida is a group of crabs, ranked as a section. It contains the single superfamily Cyclodorippoidea, which holds three families, Cyclodorippidae, Cymonomidae and Phyllotymolinidae....
, may be collected together into the Podotremata
Podotremata
In some taxonomic systems, Podotremata is the smaller of the two sections making up the crabs . Morphological and molecular analyses do not reveal a monophyletic Podotremata, and so the most recent classifications divide "Podotremata" into three sections: Dromiacea, Cyclodorippoidea and...
, each at the rank of subsection; morphological and molecular evidence argue against such a grouping.
The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of Dromiacea resemble those of the Anomura
Anomura
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans includes the word crab, all true crabs are in the sister group to the Anomura, the Brachyura .-Description:The name Anomala reflects the unusual variety of forms in this group;...
more closely than those of other crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s. This may simply reflect their basal position
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
in the crab phylogeny.
The fossil record of Dromiacea reaches back at least as far as the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, and, if Imocaris is indeed a member, into the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
.
The superfamily Eocarcinoidea
Eocarcinoidea
Eocarcinoidea is a family of fossil decapod crustaceans. Formerly thought to be the earliest true crabs, they are now thought to be the oldest members of the Anomura. Two species are included, each in its own family: Eocarcinus praecursor and Platykotta akaina ....
, containing Eocarcinus
Eocarcinus
Eocarcinus praecursor is a Jurassic species of decapod crustacean, sufficiently distinct from its relatives to be placed in its own family...
and Platykotta
Platykotta
Platykotta akaina is a species of decapod crustacean from the Triassic of the United Arab Emirates. It is the oldest known fossil from the infraorder Anomura, and is most closely related to Eocarcinus praecursor.-Stratigraphy:The holotype of P...
, was previously considered to be a member of the Dromiacea, but has since been transferred to the Anomura
Anomura
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans includes the word crab, all true crabs are in the sister group to the Anomura, the Brachyura .-Description:The name Anomala reflects the unusual variety of forms in this group;...
.